Search results for "Hydrogen"
showing 10 items of 4254 documents
Structural studies on 2-pyridyl complexes of the platinum triad metals. The crystal and molecular structure of the 2-pyridylium derivative trans-[PdC…
1991
Abstract In solution, the complex trans -[PdCl(C 5 H 4 N C 2 )(PMe 2 Ph) 2 ] ( 1 ) is in equilibrium with a small amount of the binuclear species [{PdCl(μ-C 5 H 4 N C 2 , N )(PMe 2 Ph)} 2 ] ( 2 ), which can be isolated upon recrystallization. The compound 1 is easily N-protonated by HClO 4 to the 2-pyridylium product trans -[PdCl(C 5 H 5 N C 2 )(PMe 2 Ph) 2 ]ClO 4 ( 3 ), which crystallizes in the orthorhombic space group P2 1 2 1 2 1 , with cell parameters a =15.761(3), b =14.369(2), c =11.132(2) A and Z =4. The X-ray crystal structure analysis of 3 , using 3744 observed reflections in the refinement and resulting in a final R value of 0.0298, shows that the coordination around palladium…
Composés métallocèniques chalcogènés. Action des dihydrures de zirconocène et de hafnocène sur le soufre, le sélénium et le tellure
1989
Resume Dimeric zirconocene and hafnocene dihydrides [(η 5 -RC 5 H 4 ) 2 M(H)(μ-H)] 2 (M = Zr, Hf) react with grey selenium or tellurium to afford the known four-membered bimetallacyclic compounds [(η 5 -RC 5 H 4 ) 2 M(μ-E)] 2 (E = Se, Te) as the sole organometallic products. In the case of sulfur the first step of the reaction is shown to involve the insertion of a chalcogen atom into the metal-hydrogen bonds to give the bis-hydrogenosulfide (η 5 -t-BuC 5 H 4 ) 2 M(SH) 2 (M = Zr, Hf), which reacts either with the starting dihydride to give [(η 5 -t-BuC 5 H 4 ) 2 M(μ-S)] 2 or with the unchanged sulfur to afford the metallacyclohexasulfane (η 5 -t-BuC 5 H 4 ) 2 MS 5 and hydrogen sulfide. Thes…
Binding Mode and Selectivity of a Scorpiand-Like Polyamine Ligand to Single- and Double-Stranded DNA and RNA: Metal- and pH-Driven Modulation
2017
The interaction of a polyazacyclophane ligand having an ethylamine pendant arm functionalized with an anthryl group (L), with the single-stranded polynucleotides polyA, polyG, polyU, and polyC as well as with the double-stranded polynucleotides polyA-polyU, poly(dAT)(2), and poly(dGC)(2) has been followed by UV/Vis titration, steady state fluorescence spectroscopy, and thermal denaturation measurements. In the case of the single-stranded polynucleotides, the UV/Vis and fluorescence titrations permit to distinguish between sequences containing purine and pyrimidine bases. For the double-stranded polynucleotides the UV/Vis measurements show for all of them hypochromicity and bathochromic shif…
Influence of the presence of divalent first-row transition metal ions on the structure of sodium(i) salts of 1,2,3,4-benzenetetracarboxylic acid (H4b…
2006
Three different sodium(I)-containing salts of 1,2,4,5-benzenetetracarboxylic (H4bta) of formula [Na4(bta)(H2O)12] (1), [Na2M(H2bta)2(H2O)8]·2H2O] [M = Mn (2) and Ni (3)] were synthesized and their structures were solved by single crystal X-ray diffraction methods. Compound 1 crystallises in orthorhombic system, space group Pc21b with a = 6.9997(4) A, b = 16.4260(9) A, c = 20.3312(18) A, V = 476.30(15) A3 and Z = 4. Compounds 2 and 3 crystallize in the monoclinic system, space group C2/m with a = 7.3778(4) A, b = 20.1493(6) A, c = 10.4963(4) A, β = 103.466(8)°, V = 1517.5(11) A3 and Z = 2 for 1 and a = 7.2862(4) A, b = 20.1165(7) A, c = 10.4032(3) A, β = 103.366(9)°, V = 1483.52(11) A3 and Z…
Four-, five- and six-coordinated Zn-II complexes of OH-containing ligands: Syntheses, structure and reactivity
2002
Four-, five- and six-coordinated complexes of Zn-II with OH-rich molecules possessing an ONO binding core were synthesized, characterized and their structures were established by single-crystal X-ray diffraction, The corresponding metal ion geometries were found to be distorted tetrahedral, square pyramidal and octahedral, respectively. The complexes exhibit interesting lattice structures such as layered and corrugated sheets owing to the presence of a number of weak intermolecular interactions. The five-coordinated, water-bound Zn-II complex was studied because of its putative hydrolysis property towards p-nitrophenyl acetate. (C) Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.
New complex polycyclic compounds: Synthesis, antiproliferative activity and mechanism of action
2020
Abstract Polycyclic or O-glycoconiugate polycyclic compounds 1a-g were previously tested for their in vitro antiproliferative activity. In this series of compounds, activity increases as log P decreases. Specifically, compounds 1d and 1g showed lower log P values together with the best antiproliferative profiles. With the aim of extending our understanding of the structure–activity relationship (SAR) of this class of compounds, we prepared new polycyclic derivatives 2a-c, which bear on each of the two phenyl rings hydrophilic substituents (OH, SO2NH2 or NHCOCH3). These substituents are able to form hydrogen bonds and to decrease the partition coefficient value as compared with compound 1d. …
Stereoselective Synthesis of (+)-11βH,13-Dihydroestafiatin, (+)-11βH,13-Dihydroludartin, (−)-Compressanolide, and (−)-11βH,13-Dihydromicheliolide fro…
2002
Starting from 2 and 3, obtained from santonin (1), we have synthesized natural guaianolides 4-7. Chemoselective epoxidation of 2 gave (+)-11betaH,13-dihydroestafiatin (4), and epoxidation of 3 followed by regioselective elimination of the hydroxyl group afforded (+)-11betaH,13-dihydroludartin (5). Sharpless' mild regioselective ring-opening of 4 and 5 followed by hydrogenolysis yielded (-)-compressanolide (6) and (-)-11betaH,13-dihydromicheliolide (7), respectively.
Are there dynamical effects in enzyme catalysis? Some thoughts concerning the enzymatic chemical step.
2015
Highlights • The possible role of enzymatic reaction dynamical effects is examined. • Solution reactions usefully inform the issue of dynamical effects in enzymes. • Division into regions containing and away from the transition state is important. • Motions in passage to/from the transition state need not lead to dynamical effects. • Transition State Theory is usually a reasonable description of enzyme kinetics.
CO2 Fixation by Cu2+ and Zn2+ complexes of a terpyridinophane aza receptor. Crystal structures of Cu2+ complexes, pH-metric, spectroscopic, and elect…
2006
The synthesis of the terpyridinophane-type polyamine 2,6,9,12,16-pentaaza[17]-(5,5' ')-cyclo-(2,2':6',2' ')-terpyridinophane heptahydrobromide tetrahydrate (L.7HBr.4H2O) is described. L presents six protonation constants with values in the range 9.21-3.27 logarithmic units. L interacts with Cu2+ and Zn2+ forming in both cases, neutral, protonated, and hydroxylated mono- and binuclear complexes whose constants have been calculated by potentiometry in 0.15 M NaClO4 at 298.1 K. The crystal structures of the compounds [Cu(HL-carb)(H2O)](ClO4)3.2H2O (1) and [Cu2(H2L)(CO3)]2(ClO4)8.9H2O (2) have been solved by X-ray diffraction. In 1, the metal center presents square pyramidal geometry. The base …
Natural substances (acetogenins) from the family Annonaceae are powerful inhibitors of mitochondrial NADH dehydrogenase (Complex I).
1994
Natural products from the plants of the family Annonaceae, collectively called Annonaceous acetogenins, are very potent inhibitors of the NADH-ubiquinone reductase (Complex I) activity of mammalian mitochondria. The properties of five of such acetogenins are compared with those of rotenone and piericidin, classical potent inhibitors of Complex I. Rolliniastatin-1 and rolliniastatin-2 are more powerful than piericidin in terms of both their inhibitory constant and the protein-dependence of their titre in bovine submitochondrial particles. These acetogenins could be considered therefore the most potent inhibitors of mammalian Complex I. Squamocin and otivarin also have an inhibitory constant …